Apparatus and method for drying washed objects

ABSTRACT

An apparatus and a method for drying washed objects being capable of drying the objects in a reduced period of time, effectively preventing contamination of the objects, and preventing energy loss are provided. The apparatus for drying washed objects includes a drying tank having an opening on the upper portion thereof so that the washed objects can be placed or taken out from above, and a rinsing tank formed integrally with the drying tank, and is capable of being sealed hermetically by closing the openable and closable lid. The drying tank includes a mist-straightening vane for supplying organic solvent mist at normal temperatures to the washed objects, so that the washed objects are dried by organic solvent mist emitted from the mist-straightening vane.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus and a method for dryingwashed objects, and more specifically, to an apparatus and a method fordrying washed objects being suitable for washing, rinsing, and dryingsubstrates of semiconductor wafers.

2. Description of the Related Art

Heretofore, removal of moisture entered in trenches is an importantfactor in drying of miniaturized washed objects such as wafers afterwashing of precision substrates, and thus a drying apparatus usingorganic solvent vapor is employed. An apparatus shown in FIG. 1 is knownas a drying apparatus using organic solvent vapor.

The drying apparatus 1 includes, as shown in FIG. 1, a drying tank 2being box-shape having an opening on top thereof in cross section, aheating device (heater) 3 mounted on the bottom surface 2 a of thedrying tank 2, a cooling coil 4 provided on the upper part of the dryingtank 2, a solvent trap 5 provided downwardly of the cooling coil 4, awafer placing table 7 disposed in the drying tank 2 for placing a wafer6 as a washed object thereon, and a solvent pooling section 8 disposeddownwardly of the wafer placing table 7.

The drying apparatus 1 heats organic solvent 9 charged into the dryingtank 2 to a boiling point by the heater 3 and generates organic solventvapor in the upper portion thereof. A wafer 6 already washed and rinsedwith water is then inserted and arranged in the vapor in the drying tank2. Condensation of organic solvent occurs on the surface of the wafer 6that is inserted and arranged in the drying tank 2, and then moistureattached on the surface of the wafer 6 is replaced by organic solventwhich is more likely to evaporate, whereby the wafer 6 is progressivelydried. The wafer 6 in the organic solvent vapor is gradually increasedin temperature to an evaporating point (boiling point), and then istaken out of the mist atmosphere, where attached solvent componentrapidly evaporates due to its low latent heat, to be completely dried.

The organic solvent heated and vaporized by the cooling coil 4 disposedon the upper part of the drying tank 2 is condensed and dropped in thesolvent trap 5 for recovery and reusing. Likewise, solvent includingmoisture dropped from the wafer 6 is also recovered in the solventpooling section 8.

The drying apparatus 1 in the related art demands attention to flamessince organic solvent is heated by the heater 3, and consumes a lot ofenergy because it carries out heating and cooling. In addition, itrequires a significant period of time until a vapor layer is formed bybeing heated by the heater 3, and consumes a large quantity of organicsolvent due to evaporation. Further, when the washed objects come incontact with the mist layer, heat of vapor (gas phase) is absorbed bythe washed object, thereby causing abrupt change in phase (gas phase toliquid phase) and reducing the vapor layer. Consequently, the washedobject is exposed to the atmosphere, which may easily results incontamination, insufficient drying, and so on.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide anapparatus and a method for drying washed objects being capable of dryingthe washed objects in a reduced period of time, effectively preventingcontamination of the objects, and preventing energy loss.

The apparatus for drying washed objects according to the inventionincludes a drying tank in which organic solvent mist is generated andsupplied to washed objects therein, wherein the drying tank includes amist-straightening vane for supplying organic solvent mist to the washedobjects.

The mist-straightening vane of the apparatus for drying washed objectsaccording to the invention is provided on the side wall of the dryingtank, and is provided with a plurality of fine openings on the surfacefor emitting organic solvent mist at the position upwardly of a fluidspray nozzle away from a prescribed distance S, so that a portion oforganic solvent mist that passed through the opening out of the wholepart of organic solvent mist emitted from the fluid spray nozzle isindirectly emitted.

The fluid spray nozzle of the apparatus for drying washed objectsaccording to the present invention can emit two or more different typesof fluid simultaneously.

Fluid emitted from the fluid spray nozzle of the apparatus for dryingwashed objects according to the invention includes organic solvent mistand inert gas.

The configuration of the opening of the apparatus for drying washedobjects according to the invention is chamfered configuration.

The apparatus for drying washed objects according to the inventionincludes a drying tank having an opening on top thereof so that thewashed objects can be placed or taken out from above and a rinsing tankformed integrally with the drying tank, and is capable of being sealedhermetically by closing the openable and closable lid, and the dryingtank includes a mist-straightening vane for supplying organic solventmist to the washed objects.

The drying tank of the apparatus for drying washed objects according tothe invention includes an overflow tank formed on top of the rinsingtank integrally for overflowing deionized water to be supplied into therinsing tank, and a channel for drainage from the overflowing tank isgrounded.

The apparatus for drying washed objects according to the inventionincludes cradles for placing and holding washed objects in the dryingtank and in the rinsing tank, and the cradle can be moved upward anddownward by a hoisting mechanism and can be stopped in a state in whicha part of the washed object is in contact with the fluid level directlyor indirectly.

The portion of the washed object that is immersed into the fluid levelof the rinsing tank of the apparatus for drying washed objects accordingto the invention is the portion other than the patterned surface.

A method for drying washed objects according to the invention is amethod for drying washed objects for performing drying by the use of adrying apparatus including a drying tank having an opening on topthereof so that washed objects can be placed or taken out from above,and a rinsing tank formed integrally with the drying tank, and iscapable of being sealed hermetically by closing an openable and closablelid, comprising the steps of moving a cradle for placing and holdingwashed objects upward and downward by a hoisting mechanism after thewashed object was rinsed in the rinsing tank and stopping the same in astate in which a part of the washed object is in contact with the fluidsurface directly or indirectly, performing drying process by emittingorganic solvent mist to the washed object from a fluid spray nozzleprovided on a mist-straightening vane and emitting the same in turn fromthe mist-straightening vane indirectly, draining deionized water afterthe drying step, and performing quick drying process by supplying inertgas at a high temperature into the drying tank after the draining step.

In a method for drying washed objects according to the invention, thewashed object is wet when the washed object is drawn up from the rinsingtank by the hoisting mechanism.

In a method for drying washed objects according to the invention, theinert gas is nitrogen gas (N₂) at normal temperatures or heated nitrogengas (N₂).

In a method for drying washed objects according to the invention, anorganic solvent for generating the mist of organic solvent is selectedfrom alcohols, ketones, or ethers having water solubility and capabilityof lowering surface tension of deionized water with respect to thesubstrate.

In a method for drying washed objects according to the invention, thediameter of organic solvent mist emitted indirectly from themist-straightening vane is not more than 20 μm.

In a method for drying washed objects according to the invention, theorganic solvent can be heated to temperatures within the range of 5° C.to 80° C. when it is IPA (Isopropyl alcohol).

In a method for drying washed objects according to the invention,rinsing water for performing rinsing operation in the rinsing tank ishydrogenated water.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing showing a drying apparatus in the related art;

FIG. 2 shows a drying apparatus according to an embodiment of theinvention partially in cross section;

FIG. 3 is an explanatory drawing illustrating a state in which organicsolvent mist is emitted indirectly by the use of a mist-straighteningvane;

FIG. 4 is an explanatory drawing illustrating the diameter of organicsolvent mist emitted from the mist-straightening vane and the emittingstate;

FIG. 5(a) and FIG. 5(b) are enlarged cross sectional views showing theconfigurations of the opening on the mist-straightening vane;

FIG. 6 is a drawing showing a state of transferring particles as aresult of being dried using Marangoni Effect, that is, Marangoni Drying,after being etched by DHF (HF/H₂O) (diluted hydrofluoric acid);

FIG. 7 is a graph of the increasing amount of particles in MarangoniDrying, illustrating the result after performing the steps of rinsingwith deionized water→drying, and the result after performing the stepsof etching with DHF (HF/H₂O) (diluted hydrofluoric acid)→rinsing withdeionized water→drying;

FIG. 8 is a drawing for comparing the amount of increase in particles inMarangoni Drying and drying according to the invention;

FIGS. 9(a) to 9(i) are explanatory drawings showing the drying processin a drying method according to the invention;

FIG. 10 is a time chart of the drying process according to theinvention;

FIG. 11 is an enlarged explanatory drawing of a state shown in FIG.9(e);

FIGS. 12(a) and 12(b) are explanatory drawings illustrating the amountof electrostatic charge on the surface of wafer shown in FIG. 11;

FIG. 13 is a drawing showing a state in which the diameter and thenumber of the particles of organic solvent mist M are measured by theuse of a Phase Doppler Particle Analyzer for five minutes when themist-straightening vane is used;

FIG. 14(a) is a drawing showing results of measurement in the experimentconducted in conjunction with FIG. 13, and FIG. 14(b) is a drawingshowing results of measurement of the diameter and the number ofparticles of organic solvent mist M without using the mist-straighteningvane shown in FIG. 13.

FIG. 15 is a diagrammatic sketch of a state in which electrostaticcharge is being removed;

FIG. 16 is a graph of the thickness of oxidized film on the surface ofthe silicon measured after being etched by DHF (HF/H₂O) (dilutedhydrofluoric acid) and being rinsed with hydrogenated water which isobtained by adding hydrogen water to rinsing water in the rinsing tankby the use of the drying apparatus according to the invention, and thenperformed the drying process; and

FIG. 17 is a drawing showing another embodiment of the drying apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, an embodiment of a drying apparatus and adrying method according to the invention will be described. FIG. 2 is adrawing showing a drying apparatus according to an embodiment of theinvention partly in cross section.

As shown in FIG. 2, the drying apparatus 11 includes a drying tank 30, arinsing tank 40, and a plumbing system 50. The drying tank 30 isprovided on top of the rinsing tank 40 integrally therewith. The dryingtank 30 is open on top thereof and thus the wafer W as washed objectscan be placed or taken out from above, and is capable of being sealedhermetically by closing an openable and closable lid 31. In other words,a lid packing 39 completely prevents outside air from entering therein.The openable and closable lid 31 is opened and closed by slidingmovement thereof via a guiding mechanism, which is not shown in thefigure, in the vertical direction with respect to the plane of FIG. 2.FIG. 2 shows the closed state.

The drying tank 30 and the rinsing tank 40 are constructed of membershaving non-conductive properties and corrosion resistance properties,and are box-shape opening on top in cross section. The rinsing tank 40is slightly smaller than the drying tank 30, and the upper portion ofthe rinsing tank 40 is placed into the lower portion of the drying tank30. It is for allowing deionized water in the rinsing tank 40 tooverflow.

As shown in FIG. 2, mist-straightening vanes 32 for supplying organicsolvent mist, which is IPA in this embodiment, indirectly to the wafer Was a washed object are provided on both sides of the side wall of thedrying tank 30 so as to sandwich the outer peripheral surface of thewafer W. The wafer W in the drying tank 30 is, as shown in FIG. 2,substantially circular (a part of the outer periphery is cut out to forman orientation flat), and a plurality of wafers W are disposed inparallel at regular intervals in the vertical direction with respect tothe plane of the figure. Generally, when they are semiconductor wafers,for example, 100 pieces of wafers measuring 8 inches in diameter may beplaced, though the number and the diameter may be selected asappropriate. These wafers Ware placed on the cradle 33 having foursupporting members in this embodiment. In this embodiment, the wafer Wis assumed to have 12 inches in diameter. As shown in FIG. 2, the cradle33 is capable of moving upward and downward between the rinsing tank 40and the drying tank 30 by the aid of a hoisting mechanism, which is notshown.

The mist-straightening vane 32 is formed entirely of a laterallyelongated rectangular solid as shown in FIG. 3, and has a width thatenable itself to supply organic solvent mist M, which is IPA in thiscase, to the main surfaces of the plurality of wafers W simultaneously.Formed on the surface 32F of the mist-straightening vane 32 positionedon the side of the peripheral surface of the wafer W are a plurality offine openings 32 a. The size of the opening 32 a is approximately 5 mmin this embodiment. The openings 32 a are, as shown in FIG. 4 as well,not formed on the area from the lower end of the mist-straightening vane32 (the position on which a fluid spray nozzle 34 is to be mounted) tothe point at a distance S. The organic solvent mist M of IPA is, asshown in FIG. 2 through FIG. 4, supplied by a sufficient amount in theform of high-density mist M of an organic solvent (two different typesof fluid are supplied in this embodiment) from the fluid spray nozzle 34mounted at the lower portion of the mist-straightening vane 32, filledinside the mist-straightening vane 32, and supplied from the openings 32a indirectly to the wafer W. The diameter of the emission aperture ofthe fluid spray nozzle 34 is approximately 1 mm. The organic solvent forgenerating the organic solvent mist is selected from alcohols, ketones,or ethers having water solubility and capability of lowering surfacetension of the deionized water with respect to the substrate.

Referring now to FIG. 4, the change in the state of the organic solventmist M in this embodiment will be described in detail. The organicsolvent mist M emitted from an emission aperture at the tip of the fluidspray nozzle 34 and in the region a, that ranges from the lower end tothe position at a distance S (about 100 mm in this embodiment), isfilled with organic solvent mist ML of at least 20 μm. On the otherhand, the region b upwardly of the region a is filled with mixture oforganic solvent mist ML of at least 20 μm and organic solvent mist MS ofless than 20 μm. The mixed organic solvent mist ML and MS arestraightened at the openings 32 a on the mist-straightening vane 32, andonly the organic solvent mist MS passes therethrough and is supplied tothe wafer W. The organic solvent mist ML of at least 20 μm is condensedinside the mist-straightening vane 32 and discharged from a dischargeport 32 b shown in FIG. 3.

FIG. 13 is a drawing showing a state in which the diameter and thenumber of particles of organic solvent mist M when using themist-straightening vane 32 are measured by the use of a Phase DopplerParticle Analyzer for five minutes, FIG. 14(a) is a drawing showingresults of experiment conducted in conjunction with FIG. 13, and FIG.14(b) is a drawing showing results of measurement of the diameter andthe number of particles of the organic solvent mist M without using themist-straightening vane shown in FIG. 13. The lateral axes in FIG. 14(a)and FIG. 14(b) represent the diameter of the particle of the mist (μm)and the vertical axes thereof represent the number of mist particles.

As shown in FIG. 13 and FIG. 14, when the mist-straightening vane 32 wasnot used, the mist diameter showing the peak of the number of mistparticles was in the vicinity of 8 μm, and the average mist particlediameter was 11.5 μm. Many large particles measuring at least 10 μm indiameter were also detected.

On the other hand, when the mist-straightening vane 32 was used, themist diameter showing the peak of the number of mist particles was inthe vicinity of 5 μm, and the average mist particle diameter was 6.4 μm.Large particles measuring at least 10 μm in diameter were found littleor nothing.

As is described thus far, the invention is contemplated based on thefact that it is important to supply organic solvent mist M uniformly tothe space between the wafers W in order to dry a plurality of wafers Wsimultaneously, and thus organic solvent mist M having smaller diameteris more preferable. It is because the particles of organic solvent mistM having smaller diameter can be gasified easily in comparison with theparticles having larger diameter, and thus the rate of diffusion in theair increases. Organic solvent mist Ma shown in FIG. 4 is in the stateof being gasified.

Therefore, according to the invention, organic solvent mist M of IPA isindirectly emitted by the use of the mist-straightening vane 32 withoutheating for generating organic solvent mist M as in the related art,whereby high-securities are ensured and organic solvent mist M can besupplied immediately, thereby improving operating efficiency of theentire apparatus.

FIG. 5(a) and FIG. 5(b) are enlarged cross sectional view showing theconfiguration of the opening 32 a on the mist-straightening vane 32.

The semiconductor wafer W and organic solvent mist M of IPA have aproperty that is apt to be charged. Therefore, in the case where theedge portion of the opening 32 a is acutely angled as shown in FIG.5(a), electrostatic charge causes concentration of electric field, andthus increases probability of discharge, which results in charging ofthe wafer W by induction. Therefore, in order to prevent such acondition, the edged portion in this embodiment is not formed into anacutely angled edge as shown in FIG. 5(b), but chamfered to preventelectric field from concentration when being charged, and to reduce theprobability of occurrence the discharging phenomenon. In thisembodiment, other chamfered configuration may be employed as far as itcan reduce the probability of occurrence of the discharging phenomenon.The organic solvent mist is also referred to as IPA mist.

As shown in FIG. 2, the drying tank 30 is provided with a exhaust port36 at the upper portion thereof and a nitrogen gas supply port 37 forsupplying nitrogen gas (N₂).

The rinsing tank 40 is supplied with deionized water through thedeionized water supplying nozzle 41 for supplying deionized water asshown in FIG. 2. When deionized water supplied into the rinsing tank 40reaches to a certain level, it is stored temporarily in an overflow tank42 shown in FIG. 2 and then is overflowed through the channel with adrain valve 52. The channel with the drain valve 52 is grounded. In sucha situation, a gaseous phase portion 35 is formed in the drying tank 30.The rinsing tank 40 is provided with a drain valve 43 for drainingdeionized water at the center on the bottom thereof, so that deionizedwater in the tank is drained through the drainage duct when the drainvalve 43 is opened.

The plumbing system 50 to be connected to the drying tank 30 and rinsingtank 40 will be described below.

The plumbing system 50 includes (1) a channel for supplying nitrogen gas(N₂) to the nitrogen gas supply port 37, (2) a channel for supplying twotypes of fluids, IPA as an organic solvent and nitrogen gas (N₂), to thefluid spray nozzle 34, (3) a channel for exhausting air from the dryingtank 30, (4) a channel for supplying deionized water into the rinsingtank 40, (5) a channel for drainage from the overflow tank 42, and (6) achannel for draining deionized water in the rinsing tank 40. Control ofthe plumbing system 50 is performed by a control unit which is not shownin the figure.

(1) In the channel for supplying nitrogen gas (N₂) to the nitrogen gassupply port 37, nitrogen gas (N₂) at ordinary temperatures supplied whenthe valve 53 is in the opened state (ON) is heated by a heater 54 andsupplied to the nitrogen gas supply port 37 through a filter 55.Nitrogen gas (N₂) at high temperatures heated by the heater 54 is usedfor quickly drying the wafer W as a washed object in the drying tank 30.In the cannel for supplying nitrogen gas (N₂) to the nitrogen gas supplyport 37, as shown in FIG. 2, when the aforementioned valve 53 is in theopened state (ON), the other valve 56 is in the closed state (OFF). Incontrast to it, when the valve 53 is in the closed state (OFF), thevalve 56 is in the opened state (ON), and nitrogen gas (N₂) at ordinarytemperatures is supplied to the drying tank 30 through the filter 55.Even when the wafer W as a washed object does not exist in the dryingtank 30, clean nitrogen gas (N₂) at ordinary temperatures is suppliedinto the drying tank 30 so that the gaseous phase portion 35 iscompletely filled.

The valve 53, the valve 56, and the heater 54 can be controlled by thecontrol unit which is not shown, so that switching of the valve 53 andthe valve 56, and the temperature of the heater 54 are controlled.

(2) The channel for supplying two different types of fluid, IPA as anorganic solvent and nitrogen gas (N₂), to the fluid spray nozzle 37includes an IPA tank 59 for storing IPA, a pump 60 for supplying IPAfrom the IPA tank 59, a filter 61 for cleaning supplied IPA, a valve 62,a valve 63, an IPA heater 67 for heating IPA, and a valve 57 forsupplying nitrogen gas (N₂), and a filter 58. Two types of fluid, IPA asan organic solvent and nitrogen gas (N₂), are supplied to the fluidspray nozzle 34 simultaneously. Nitrogen gas (N₂) is for securingsafety. Such control is performed by the control unit which is not shownin the figure as described above.

(3) The channel for exhausting air from the drying tank 30 is forsucking and exhausting air from the exhaust port 36 with the valve 64opened (ON).

(4) The channel for supplying deionized water into the rinsing tank 40is for supplying deionized water from the deionized water supplyingnozzle 41 with the valve 51 opened (ON).

(5) The channel for drainage from the overflow tank 42 is for drainingdeionized water overflowed from the rinsing tank 40 and IPA which is adissolved organic solvent through the drain valve 52.

(6) The channel for draining deionized water in the rinsing tank employsa drain valve 43.

The drying method using the drying apparatus of the invention ischaracterized by being a drying method which does not utilize MarangoniEffects as in the case shown in FIG. 6. FIG. 6 is a drawing showing astate of transferring particles as a result of being dried usingMarangoni Effects, that is, Marangoni Drying, after being etched by DHF(HF/H₂O) (diluted hydrofluoric acid), and FIG. 7 is a graph of theincreasing amount of particles in Marangoni Drying, illustrating theresult after performing the steps of rinsing with deionizedwater→drying, and the result after performing the steps of etching withDHF (HF/H₂O) (diluted hydrofluoric acid)→rinsing with deionizedwater→drying. The concentration of IPA in FIG. 6 is CI>CII, and thesurface tension is rI<rII. When the concentration of IPA is CII=CIII,the surface tension is rII=rIII. C represents the concentration of IPA,r represents the surface tension, and Roman numbers I to III representthe position shown in FIG. 6.

As is clear from FIG. 6, IPA gas (not IPA mist) is supplied between abare wafer and a wafer with an oxidized film, and when deionized wateris withdrawn downward in this state, water is apt to be stuck on thebare wafer facing toward the wafer with an oxidized film by MarangoniForce, and the particles are also apt to be stuck on the bare wafer.Therefore, as is clear from FIG. 7, the number of particles increasesabruptly when dried by Marangoni Drying after being etched by DHF(HF/H₂O) (diluted hydrofluoric acid).

FIG. 8 is a graph for comparing the drying method using the dryingapparatus according to the invention, and the drying method usingMarngoni Effects, and an object of the invention is to provide a dryingmethod in which increase in the number of particles due to MarangoniDrying after being etched by DHF (HF/H₂O) (diluted hydrofuoric acid) asshown in FIG. 6 and FIG. 7 is prevented.

Referring now to FIG. 9 through FIG. 12, the drying method according tothe invention will be described. FIG. 9 is an explanatory drawingshowing the drying process in the drying method according to theinvention, FIG. 10 is a time chart of the drying process according tothe invention, FIG. 11 is an enlarged explanatory drawing of a stateshown in FIG. 9(e), and FIG. 12 is an explanatory drawing illustratingthe amount of electrostatic charge on the surface of the wafer shown inFIG. 11.

(1) Drying Step Shown in FIG. 9(a)

FIG. 9(a) shows a state where no wafer W exists in the drying apparatus11. As shown in the step 1 in FIG. 10, in a state in which the openableand closable lid 31 is closed, and deionized water is supplied from thedeionized water supply channel (4) to the rinsing tank 40 for overflowrinsing, nitrogen gas (N₂) is supplied from the nitrogen gas (N₂) supplychannel (1) through the valve 56, the filter 55, and the nitrogen gassupply port 37 to the drying tank 30, and simultaneously, air is suckedand exhausted from the exhaust channel (3) with the valve 64 opened, andIPA is circulated in the IPA supply channel (2) with the valve 63 closedand the valve 62 opened. At this time, the cradle 33 is lowered into therinsing tank 40.

(2) Drying Step Shown in FIG. 9(b)

The openable and closable lid 31 of the drying tank 30 is opened and awashed object such as a wafer W that is washed or rinsed is stored,placed and supported on the cradle 33 by means of a carrying unit, notshown. The openable and closable lid 31 is constructed to be openableand closable automatically or manually when the wafer was a washedobject is loaded in or unloaded from the drying tank 30 or the rinsingtank 40. As shown in the step 2 in FIG. 10, all the points such asoverflow rinsing, supply of nitrogen gas (N₂), suction exhaust, and IPAcirculation are identical to FIG. 9(a) other than the fact that theopenable and closable lid 31 is opened and the cradle 33 is movedupward.

Subsequently, when the washed object such as a wafer W is placed on thecradle 33, the carrying unit, not shown, is retracted from the dryingtank 30, the openable and closable lid 31 is closed, and the cradle 33is lowered into the rinsing tank 40 together with the wafer W.

(3) Drying Step Shown in FIG. 9(c)

FIG. 9(c) shows a rinsing step using deionized water performed in therinsing tank 40. The valve 51 on the channel (4) shown in FIG. 2 isopened, and deionized water is supplied from the deionized watersupplying nozzle 41 for overflow rinsing. The openable and closable lid31 is closed, the cradle 33 is in the lowered state, and the states ofsupply of nitrogen gas (N₂), suction exhaust, IPA circulation areidentical to the case shown in FIG. 9(b). The overflow rinsing isperformed at a rate of about 30 litters/min for about 60 seconds.

(4) Drying Step Shown in FIG. 9(d)

FIG. 9(d) shows a state in which the cradle 33 on which the wafer W isplaced in the rinsing tank 40 is moved upward after overflow rinsing inthe step 3 in FIG. 10 is finished. As is clear from FIG. 10, the processin the step 4 is identical to that in the step 3 except for upwardmovement of the cradle 33. The period of time required for moving thecradle 33 upward is approximately 30 seconds as shown in the step 4 inFIG. 10. The upward movement of the cradle 33 will be stopped in a statein which the lower surface of the wafer W is slightly immersed in thefluid surface in the rinsing tank 40, as is clear from FIG. 9(e). Thoughthe stop position of the cradle 33 is controlled by a control unit whichis not shown in the figure, the stop position is set in advance. Whenthe washed object is a wafer W, since the wafer W is provided with apattern on the surface thereof, it is stopped in a state in which theportion of the wafer W in the vicinity of the outer periphery thereof,which is not formed with a pattern, comes into contact with the fluidsurface. In this case, the wafer W as a washed object is still wet whenit is drawn upward from the rinsing tank 40 by the hoisting mechanism.

Though a state in which the lower surface of the wafer W is directly incontact with and immersed into the fluid surface in the rinsing tank 40has been described, the inventor verified that electrostatic charge canbe removed by bringing the wafer W into indirect contact with the fluidsurface in the rinsing tank 40 by the use of a draining rod for securingindirect contact between the wafer W and rinsing water as shown in FIG.15, and allowing water to drop via the draining rod. FIG. 15 is adiagrammatic sketch of a state in which electrostatic charge is beingremoved.

(5) Drying Step Shown in FIG. 9(e)

FIG. 9(e) corresponds to the step 5 in FIG. 10, in which the valve 62shown in FIG. 2 is closed and the valve 63 is opened, and the valve 57is opened to supply two types of fluid, IPA as an organic solvent andnitrogen gas (N₂), from the fluid spray nozzle into the drying tank 30.Such IPA mist supply continues for approximately 120 seconds as shown inFIG. 10. In this case, the IPA heater 67 can be heated to thetemperature in the range between 5° C. and 80° C., and the IPA heater 67is turned ON when supplying IPA mist.

As shown in FIG. 11, the IPA mist atmosphere in the drying tank 30 isapt to become positively charged, and thus the wafer W is apt to becharged as well. Accordingly, in the drying method of the invention, asshown in FIG. 11, residual water on the wafer W with IPA mist dissolvedtherein runs along the surface on the wafer W downwardly and drops intodeionized water in the rinsing tank 40 and dissolves therein. Sinceoverflow rinsing is performed as is clear from the step 5 in FIG. 10,the overflow tank 42 is grounded via a drainage channel (FIG. 2 (5)) andthus positive electrostatic charge is removed.

FIG. 12(a) is a graph illustrating measured amount of electrostaticcharge on the wafer surface when it is dried without immersing the lowersurface of the wafer W in the fluid surface in the rinsing tank 40according to a method other than the invention. Such measurement isperformed during the drying process shown in FIG. 9(e) and in the step 5in FIG. 10. Change in the amount of electrostatic charge shown in FIG.12(a) is caused by the phenomenon in which electrostatic charge istemporarily removed from the wafer W when residual water on the surfaceof the wafer W and IPA drop into rinsing water in the rinsing tank 40.

FIG. 12(b) is a graph illustrating measured amount of electrostaticcharge on the surface of the wafer when the wafer W is dried with thelower surface of the wafer W directly immersed into the fluid surface inthe rinsing tank 40 according to the invention. Such measurement isperformed during the drying process shown in FIG. 9(e) and in the step 5in FIG. 10, and it is recognized that the amount of electrostatic chargeon the surface of the wafer is removed according to the invention. Thesame effects can be obtained when removal of electrostatic charge isperformed without immersing the lower surface of the wafer W directlyinto the fluid surface in the rinsing tank 40, but performed indirectlyby the use of drainage rod as is described in conjunction with FIG. 15.

(6) Drying Step Shown in FIG. 9(f)

FIG. 9(f) shows a state in which the valve 63 shown in FIG. 2 is closed,and the valve 62 in the same figure is opened to stop supply of IPA mistand thus IPA is circulated. Subsequently, the drain valve 43 is openedto drain deionized water in the rinsing tank 40. The period of timerequired for processing is approximately 10 seconds. As shown in thestep 6 in FIG. 10, nitrogen gas (N₂) is supplied through the nitrogengas (N₂) supply channel (1), the valve 56, the filter 55, and thenitrogen gas supply port 37 into the drying tank 30, and in the exhaustchannel (3), the valve 64 is opened and thus sunction exhaust is beingperformed.

(7) Drying Step Shown in FIG. 9(g)

FIG. 9(g) corresponds to the step 7 in FIG. 10, and illustrates a statein which the valve 56 is closed to stop supply of nitrogen gas (N₂) atordinary temperatures, the valve 53 is opened, and nitrogen gas (N₂) isheated by the heater 54 to supply nitrogen gas (N₂) at high temperaturesinto the drying tank 30. The period of time required for supplyingnitrogen gas (N₂) at high temperatures is approximately 150 seconds, andduring which the surface of the wafer W in the drying tank 30 is quicklydried.

(8) Drying Step Shown in FIG. 9(h)

FIG. 9(h) shows a state in which the valve 53 is closed and the heater54 is turned off under the atmosphere of high-temperature nitrogen gas(N₂) in the previous step, and then the valve 56 is opened to supplynitrogen gas (N₂), which is inert gas at ordinary temperatures, into thedrying tank 30 to return the interior of the drying tank 30 to ordinarytemperatures, which is so called “cooling down”. The period of timerequired for this process is approximately 30 seconds. The interior ofthe drying tank 30 is maintained in an inert gas atmosphere by nitrogengas (N₂), which is an inert gas at ordinary temperatures, being suppliedfrom the nitrogen gas supply port 37, so that the surface of the wafer,for example, a silicone (Si) can be prevented from reoxidization.

(9) Drying Step Shown in FIG. 9(i)

FIG. 9(i) shows a state in which the openable and closable lid 31 isopened to carry the dried wafer W placed on the cradle 33 out of thedrying tank 30 with the carrying unit, not shown, as shown in the step 9in FIG. 10.

As is described above, the drying apparatus according to the inventionis constructed of the drying tank 30 and the rinsing tank 40, and thusthe space can be saved. Further, since organic solvent mist is notsupplied in the step of drawing the wafer W up from the rinsing tank 40according to the invention, Marangoni Effects do not occur at theinterface between the wafer W and rinsing water in the rinsing tank 40.Therefore, particle transfer does not occur neither. In the dryingmethod according to the invention, gas at ordinary temperatures is usedas nitrogen gas (N₂), which is an inert gas in order to maintain theatmosphere at ordinary temperatures. Therefore, nitrogen gas (N₂) as aninert gas used in the step of vaporizing organic solvent (IPA) fordrying (the step 7 in FIG. 10) is preheated, because it enables quickdrying. Temperatures to be heated are preferably between 20° C. and 100°C. according to the exemplified experiment. However, gas at ordinarytemperatures, which is not heated, may be used depending on the type ofwashed objects. Though nitrogen gas (N₂) is used as an inert gas in thisembodiment, argon gas may be used as an alternative. Further more,according to the invention, adherence of particles from the wafer havingan oxidized film or a pattern may be prevented, and reoxidization of thesurface of the silicon (Si) can be prevented.

FIG. 16 is a graph of the thickness of oxidized film on the surface ofthe silicon measured after being etched by DHF (HF/H₂O) (dilutedhydrofluoric acid) and being rinsed with hydrogenated water which isobtained by adding hydrogen water to rinsing water in the rinsing tankby the use of the drying apparatus according to the invention and thenperformed the drying process. The lateral axis represents rinsing time(min), and the vertical axis represents the thickness of naturaloxidized film (angstrom).

As shown in FIG. 16, though the thickness of oxidized film formed on thesurface of the silicon increases in accordance with the rinsing time,the inventor verified that development of natural oxidized film issuppressed when rinsed with hydrogenated water in comparison with thecase of being rinsed with ultra pure water having an O₂ concentration of15 ppb. It is considered to be because bonding between silicon (Si) andhydrogen is promoted due to existence of hydrogen in rinsing water andthus bonding between silicon (Si) and oxygen is hindered. From thesereasons, using hydrogenated water which is obtained by adding hydrogenwater to rinsing water suppresses development of natural oxidized filmon the surface of the silicon and prevents formation of watermark.Therefore, with the drying apparatus and the drying method according tothe invention, hydrogenated water may be selected as rinsing water.

Referring now to FIG. 17, another embodiment of the drying apparatusaccording to the invention will be described. Since basic constructionsand functions are substantially identical to the apparatus shown in FIG.2, only the different points will be described.

As shown in FIG. 17, since the drying apparatus 30 has a constructionthat does not have the rinsing tank 40, it does not have the overflowtank 42. Therefore, the drying apparatus shown in FIG. 17 is intended toperform only drying operation for the wafer W as a washed object whichhas rinsed already in the previous step.

According to the invention, particle transfer due to Marangoni Forcedoes not occur, and oxygen is purged because an inert gas atmosphere isformed by nitrogen, whereby formation of watermark is prevented andimprovement of productivity is realized. Further, since the process isperformed in a sealed structure, contamination of the washed object canbe prevented.

As is described thus far, according to the present invention, sinceorganic solvent mist is indirectly emitted, the diameter of organicsolvent mist can be reduced. Further, according to the invention,particle transfer due to Marangoni Force does not occur, and oxygen ispurged because an inert gas atmosphere is formed by nitrogen, wherebyformation of watermark can be prevented and improvement of productivityis realized. Furthermore, since the process is performed in a sealedstructure, contamination of the washed object can be prevented.

What is claimed is:
 1. An apparatus for drying a washed object,comprising: a drying tank; a mist-straightening vane provided in thedrying tank, said mist-straightening vane comprising a side surfacewhich faces the washed object, and said side surface including a solidlower section and an upper section having a plurality of fine openings;and a fluid spray nozzle provided in a lower portion of themist-straightening vane for supplying an organic mist; wherein a portionof the organic mist supplied by the fluid spray nozzle is emittedthrough the plurality of fine openings in the upper section of said sidesurface of the mist-straightening vane toward the washed object.
 2. Theapparatus according to claim 1, wherein the mist-straightening vane isprovided on a side wall of the drying tank.
 3. The apparatus accordingto claim 1, wherein the fluid spray nozzle is adapted to emit at leasttwo different types of fluid simultaneously.
 4. The apparatus accordingto claim 1, wherein the fluid spray nozzle is adapted to emit organicsolvent mist and inert gas.
 5. The apparatus according to claim 3,wherein the at least two different types of fluid comprise organicsolvent mist and inert gas.
 6. The apparatus according to claim 1,wherein the plurality of fine openings comprise chamfered inner sidesurfaces.
 7. The apparatus according to claim 1, wherein the solid lowerportion of the side surface of the mist-straightening vane has a heightof 100 mm.
 8. An apparatus for drying a washed object, comprising: adrying tank having an opening in an upper portion thereof for insertingand removing the washed object; a rinsing tank formed integrally withthe drying tank; a lid which is adapted to be hermetically sealed whenclosed; an overflow tank formed integrally with the drying tank and therinsing tank and provided externally to the rinsing tank; and amist-straightening vane provided in the drying tank, saidmist-straightening vane comprising a side surface which faces the washedobject, and said side surface including a solid lower section and anupper section having a plurality of fine openings; wherein the overflowtank is adapted to hold deionized water which overflows out of therinsing tank.
 9. The apparatus according to claim 8, further comprisinga channel for draining the overflow tank, wherein the channel isgrounded.
 10. The apparatus according to claim 8, further comprisingcradles for placing and holding the washed object, wherein the cradlesare movable between the drying tank and the washing tank by a hoistingmechanism, and the cradles are adapted to be stopped when a portion ofthe washed object is in contact with the fluid level.
 11. The apparatusaccording to claim 10, wherein the cradles are adapted to prevent apatterned surface of the washed object from coming in contact with thefluid level.